Role of 'good' cholesterol probed

6th December 2011

While plenty of studies have shown that high levels of high density lipoprotein (HDL) benefit heart health, scientists are still unsure as to whether or not lacking HDL is bad for the heart, according to a recent Danish study.

Having a gene mutation that lowers one's levels of HDL seems to come with having an average risk of heart attack.

Christopher Cannon, a professor of medicine at Harvard Medical School, who was not involved in the study, said that people with low levels of the so-called 'good' cholesterol often also had a lot of other issues related to heart disease.

The lead researcher, Ruth Frikke-Schmidt said that the finding was statistical in nature, and that there was no cause-and-effect basis for studying low levels of HDL.

Cannon said that, in general, people with low HDL often had high blood pressure, may have diabetes, and sometimes had higher levels of LDL, the so-called 'bad' cholesterol.

For the study, the researchers analysed data from about 70,000 people in Denmark, and found that generalisations about low levels of HDL were generally true.

But since having a gene mutation that lowers HDL does not confer a greater risk of heart attack, the researchers believe that researchers may need to conduct further study as to the effect of HDL levels on heart disease.

Cannon said that the study showed scientists re-thinking their previous assumptions about heart health, and that there were so many question marks as to how things really worked that medical professionals needed to just wait and see what researchers found.

For the study, the researchers needed to try to statistically isolate the effects of HDL from other factors such as obesity and diabetes.

The HDL lowering gene, known as LCAT, occurs in about 4% of humans.

Based on those percentages, the researchers were able to calculate that, in people who did not have the LCAT variant, having 13% lower than average HDL represented an increased heart attack risk of 18%.

Cannon said that the recent Danish study was just one of many that questioned what cardiologists had believed for decades.

The researchers wrote that some drugs currently in trial claimed to be able to raise people's levels of HDL.

They wrote that, if low HDL was not the cause of heart attacks, drug-enhanced levels of HDL may not have any effect.

Frikke-Schmidt said she believed that remnant lipoproteins were the most likely cause of increased heart attack risk, since they transported fats through the blood.